ltm4616 Linear Technology Corporation, ltm4616 Datasheet - Page 14

• Manufacturer Part Number: ltm4616
• Description: Dual 8a Per Channel Low Vin Dc/dc ?module
• Manufacturer: Linear Technology Corporation

LTM4616
between 70% and 130% of the nominal frequency. This
has the benefi t of spreading the switching noise over
a range of frequencies, thus signifi cantly reducing the
peak noise. Spread spectrum operation is disabled if
CLKIN is tied to ground or if it’s driven by an external
frequency synchronization signal. A capacitor value
of 0.01μF to 0.1μF be placed from the PLLLPF pin to
ground to control the slew rate of the spread spectrum
frequency change.
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK pin. The output can be tracked up and
down with another regulator. The master regulator’s output
is divided down with an external resistor divider that is the
same as the slave regulator’s feedback divider to implement
coincident tracking. The LTM4616 uses an accurate 10k
resistor internally for the top feedback resistor. Figure 5
shows an example of coincident tracking:
14
APPLICATIONS INFORMATION
Slave = 1+
R
10k
Figure 4. Normalized Input RMS Ripple Current vs Duty Factor for One to Six Channels (Phases)
TA
• V
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
TRACK
0
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
DUTY FACTOR (V
V
V
reference voltage. When the Master’s output is divided
down with the same resistor values used to set the slave’s
output, then the slave will coincident track with the master
until it reaches its fi nal value. The master will continue to
its fi nal value from the slave’s regulation point. Voltage
tracking is disabled when V
Figure 5 will be equal to R
The track pin of the master can be controlled by an external
ramp or by R
RC ramp time can be programmed using equation:
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the master’s
track pin. As mentioned above, the TRACK pin has a control
range from 0V to 0.596V. The master’s TRACK pin slew
O
TRACK
TRACK
/V
t = – ln 1–
IN
)
has a control range of 0V to 0.596V, or the internal
is the track ramp applied to the slave’s track pin.
SR
and C
0.596V
V
IN
SR
in Figure 5 referenced to V
4616 F04
TRACK
• R
FB
for coincident tracking.
SR
is more than 0.596V. R
• C
SR
IN
. The
TA
4616f
in